My sense is that he was known to frequent PBS viewers (I remember him from before 2010) — but the whole Chia-fro thing and "happy clouds" or whatever meme-like thing that comes to mind definitely took him to the mainstream crowd with the internet.
I present the evidence of Family Guy episode _Fifteen Minutes of Shame_ airdate April 25, 2000 which had a Bob Ross bit. Bob Ross was part of the cultural zeitgeist long before the 2010s Internet memes. That has brought a new generation to him, but that's just bringing GenZ in line with the others.
I think a lot of people who were or had kids pre-internet streaming probably watched PBS, at least sometimes.
Sesame Street, Mr. Rogers, Reading Rainbow, Joy of Painting, Arthur, Bill Nye, Barney, Teletubbies, etc.
It's not like there were a lot of TV choices for kids if their parents couldn't afford cable (and some stations like Cartoon Network didn't even exist until 1992+, I think even Disney Channel was a premium channel like HBO).